The present invention is related to a method for the operation of a wind energy plant with a synchronous generator and a superimposition gearbox.
From an overview article “Drehzahlvariable Windkraftanlagen mit elektrisch geregeltem Überlagerungsgetriebe” by P. Caselitz et al., Konferenzband “DEWEK '92”, p. 171-175, the entire contents of which is incorporated herein by reference, the use of electrically controlled superimposition gearboxes for the rotational speed variable operation of wind energy plants is put forward. Caselitz et al. point out that in this conception, the rotational speed variability is not realised in the electric part, but in the mechanical part of the plant. For this purpose, a superimposition gearbox is provided which has a third shaft, by which the gear ratio between rotor and generator can be varied on the wind energy plant. The relation between the rotational speeds of the three shafts can be summarised as follows:i1ωR−i2ωC−ωG=0 ,wherein i1 and i2 are gear ratios predetermined by the construction and ωR designates the rotational speed of the rotor, ωC the rotational speed on the third shaft of the superimposition gearbox and ωG the generator rotational speed. For driving the third shaft of the superimposition gearbox, an electric drive is normally used. The use of a power converter fed asynchronous machine with squirrel-cage armature is proposed by Caselitz et al.
From the equation at hand it is directly obvious that at connected generator with constant rotational speed ωG a variable rotor velocity ωR (t), through changing wind conditions and other boundary conditions for instance, can be compensated by an adaptation of the rotational speed at the third shaft, wherein here, a torque is guided to the generator via the third shaft or is guided from the rotor into the third shaft.
From DE 103 61 443 B4, the entire contents of which is incorporated herein by reference, a wind energy plant is known which has a rotational speed constant, grid-coupled generator. A controller with three controlling levels is provided in order to control the wind energy plant in the partial load region. In the first controlling level, the input shaft of a power-branching gearbox is driven by the wind rotor. In one power branch, a hydrodynamic speed transformer with guide wheel and guide vanes is provided. Further, a reaction member is provided in one power branch, which causes a power reflux to the power-branching gearbox via the other power branch. An improved control in a wind energy plant with a superimposition gearbox is said to be the advantages of this realisation of a wind energy plant.
From DE 103 57 292 B4, the entire contents of which is incorporated herein by reference, a method for controlling a drive train of a wind energy plant with rotational speed guiding is known, wherein the rotational speed guiding takes place via a power-branching gearbox and a hydrodynamic speed transformer with variable-pitch guide vanes. The speed transformer with variable-pitch guide vanes comprises a pump wheel, a turbine wheel and an adjustable reaction member, and thus it permits rotational speed guided control of the wind energy plant at constant rotational speed for the electric generator.
From EP 1 283 359 A1, the entire contents of which is incorporated herein by reference, a wind energy plant with a superimposition gearbox is known. The controlling shaft for the adjustment of the gear ratio on the superimposition gearbox is driven by an electric machine, in order to keep a rotational speed at the generator constant or within a certain range. For this purpose, the electric machine can be driven as a generator and as a motor as well.
The present invention is based on the objective to provide a method for the operation of a wind energy plant, which permits a high degree of grid compatibility and grid availability by simple means.